This invention relates to a small-sized coil unit, and has particular application to such a unit used for thin meters, such as watches.
An example of a known, conventional coil unit used for the same purposes is assembled by oppositely fitting on a coil (from both ends) a pair of outer cores each of which integrally consists of an axially projecting bobbin core, a bottom disk, and outer cores having two notches. The lead-in wires of the coil are led through the notches.
Such a known coil unit occupies a greater vertical space, since it is assembled into a cylindrical form by abutting a pair of pot-shaped cores in the axial direction, and then mounting them uprightly on a mounting or base plate. The mounted unit has impeded the reduction of the size of meters which employ such a coil unit because of its size. For instance, in the manufacture of wrist watches requiring a reduction in the thickness of the watch and extremely small inductors, such a conventional coil unit is unsatisfactory. The conventional coil unit also has the disadvantage that, in connecting the lead-in wires to external terminals or a printed circuit, the wires have to be wound around the terminals or printed circuit prior to soldering. Further, connecting the lead-in wires to external terminals requires intricate and difficult procedures, such as preparatory soldering, to secure reliable soldering. There is also the possibility that the lead-in wires may be damaged or cut during transportation, since they are externally exposed.
Accordingly, an object of the present invention is to provide an extremely small-sized coil unit which is ideal for use as an ultrasmall inductor and which overcomes the above disadvantages. This object is achieved through use of a coil unit formed of a coil-wound inner core partially circumferentially encased by an outer core. The coil unit is preferably mounted on a plate with the outer core externally exposed and covering the lead-in wires to the coil which are adhered to contacts on the plate.
The invention will be more completely understood by referring to the following detailed description.